Sequencing polynucleotides using nanopores is provided herein. A polynucleotide is disposed through a nanopore's aperture such that its 3′ end is on the nanopore's first side and its 5′ end is on the nanopore's second side. On the nanopore's first side, a duplex with the polynucleotide is formed. The duplex is extended by adding a nucleotide to the duplex's 3′ end. A force is applied disposing the duplex's 3′ end within the aperture. The nanopore inhibits the duplex's 3′ end from translocating to the nanopore's second side. A value of an electrical property of the duplex's 3′ end and a single-stranded portion of the polynucleotide is measured. The nucleotide at the 3′ end of the duplex is identified using the measured value. Additional nucleotides are identified by repeating these operations, then the duplex is dissociated and the polynucleotide is resequenced by repeating these operations.